As with many parasites, the protozoan Leishmania has evolved an intricate life cycle in order to support its physiological needs and to evade host defense mechanisms. Surface proteins undoubtedly play a significant role in the initiation of an infection and in the survival of Leishmania in different host environments. The goal of this project is to study the genes encoding specific Leishmania surface proteins and the developmental regulation of their expression. Using oligonucleotide probes based on partial amino acid sequence, the gene for the major 63,000 dalton surface protein of one Leishmania species will be cloned and analyzed in terms of its genomic sequence, mRNA sequence, genomic organization, and stage-specificity of transcription. Homologous surface protein genes from additional Leishmania species will then be cloned and sequenced. Comparison of these sequences will provide detailed information on conserved and non-conserved regions of the proteins which may reflect more or less important structural regions. If time permits, oligonucleotide and antibody probes will be developed for screening libraries for other Leishmania surface proteins. Comparison of structural features of more than one developmentally regulated surface protein gene and its mRNA may provide information on the coordinate control of gene expression in the differentiating Leishmania. Cloned genes will be expressed in bacteria and antibodies raised against these recombinant antigens will be used to confirm the surface localization of the cloned gene product. Selected cloned gene products will be tested as potential immunogens.